120 [Senatk 



This beautiful species of Caltmenb will be recognized by the form of the gla- 

 bella and the shallow furrows, which leave the lobes flattened, and not convex and 

 rounded as in the other American species of the genus The minute spine at the 

 posterior angle is a well-marked and peculiar feature. 



Geological formation and locality. In the calcareous shales of the age of the 

 Hudson-river group near Oxford, Ohio. The specimens were received from David 

 Christy, esq., of Cincinnati, to whom I have been indebted for many other fossils 

 from the same and other formations. . 



PROETUS PARTIUSCULUS (n.s.). 



Body small, ovate, the head broader and the thorax narrowing behind : cephalic 

 shield margined in front and at the sides by a distinct borderland the posterior 

 angles produced in small spiniform processes which reach to the fourth or fifth 

 articulation of the body. Glabella short, ovate, gibbous, a little concave at the 

 base, without visible lobes : dorsal furrow narrov^ Eyes close to the glabella, 

 and promiiUnt. 



Thorax with ten segments; the axis narrow and prominent : lateral lobes but 

 moderatel}'- convex. 



Pygidium semicircular; the axis prominent and marked by several rings, while 

 the lateral lobes are flat and marked on the upper part by about four ribs on 

 each side, with a plain expanded border around the posterior margin. 

 The length of this fossil is about one-third of an inch ; and havhig seen several 



specimens varying little in their dimensions, and none larger than the one described, 



1 am inclined to regard them as mature individuals. 



Geological formation and locality. In the calcareous shales of the Iludson-river 



group at Cincinnati, Ohio. The specimens were received from Mr. S. T. Carley. 



ORTHIS CARLEYI ( n. s.). 



Shell transversely subelliptical or subquadrate, resupinate : hinge-line less than 

 the greatest width of the shell, usually from two-thirds to three-fourths as long; 

 extremely compressed towards the cardinal extremities, and the angles rounded; 

 front margin often subtruncate; sides nearly straight, or more or less rounded. 

 Dorsal valve gibbous, arcuate and incurved at the umbo, and flattened in the 

 middle towards the front; area narrow. Ventral valve flattened near the cardinal 

 angles, elevated and obtusely pointed at the beak, and concave in the middle and 

 towards the front : beak straight, the plane of the area inclined forwards; area 

 large, triangular, with a large open foramen which reaches to the beak. 



Surface strongly striate, the niargin of each valve being marked by from fifty to 

 seventy rounded or subangular striae. Some of the striae are simple and con- 

 tinuous from the beak, the increase taking place chiefly by implantation; while 

 a small number are bifurcate. 



The length of the shells of this species is sometimes 

 an inch and a quarter or more. The specimen figured 

 has ^ length of an inch, by a width of one inch and 

 four-tenths. 



The accompanying figure is an illustration of this 

 species, looking upon the ventral valve, and, though 

 only in outline, will be sufficient to distinguish the 



fossil. GkTHIS CARLEYI. 



Geological formation and locality. In the shales cf the Hudson-river group 

 near Cincinnati, where it was originally discovered by Mr. S» T. Cablet. 



